The field of this invention is hydraulic jars for applying a jarring blow to an object stuck in a well.
In the past, hydraulic jars have been constructed with inner and outer telescopically arranged tubular elements movable longitudinally relative to each other and forming between them a single fluid chamber confining an operating fluid such as a light-weight oil or other well-known synthetic hydraulic fluid. Disposed within this fluid chamber one of the elements, usually the outer tubular body, is provided with a restricted portion and the other body is provided with a piston assembly which is adapted to move into and out of the restriction. In operation, the tubular elements are moved longitudinally relative to each other causing the piston assembly to move through the restriction with simultaneous restrained passage of the fluid from one side of the piston assembly to the other. The piston assembly movement is thus severely restricted resulting in the development of tension or compression in the operating drill string, depending upon the particular jar construction and direction of relative movement, i.e. upward or downward. As soon as the piston assembly moves out of the restriction, however, the relative movement of the tubular elements is unrestrained and the parts move suddenly to the limit of their relative movement to produce a jarring blow.
Hydraulic jars of this type have been made as two-way jars for jarring in either direction or as one-way jars for jarring in only one direction, usually on the upstroke. See, for example, U.S. Pat. Nos. 2,721,056, Re. 23,354 and 3,562,807.
Additionally, such prior jars have splined portions provided with each tubular body which are adapted for interlocking engagement to impart rotational driving forces from one to the other during normal well drilling operations. The splined portions are conventionally disposed within the operating fluid chamber of the jar so that the operating fluid may impart some lubricating action to reduce friction between the splines during rotational engagement. However, as mentioned hereinbefore, fluids conventionally employed as hydraulic fluids in such jars are light-weight oils or synthetic fluids. These conventionally employed fluids are chosen primarily for operation as hydraulic fluids, not as lubricants, and usually do not impart adequate lubrication to the splines, particularly under the heavy friction produced during normal well drilling operations.
Moreover, the engagement of the splined portions of such jars, particularly during frictional rotational engagement during normal drilling operations, inevitably results in the formation of foreign particulate matter in the form of minute metal particles or shavings which break away from the splines. This foreign particulate matter can cause jamming of the piston assembly in the restriction or otherwise permanently damage the moving parts of the jar and reduce its operational life.
Further, such prior jars usually have been constructed with jarring surfaces adjacent to or in close proximity with the piston assembly. Such construction has been found to be disadvantageous inasmuch as at least a portion of the jarring blow during a jarring operation is imparted to the piston assembly which can result in damage thereto and reduce the operational life of the jar. In addition, many of these jars have the jarring surfaces disposed in the single fluid chamber which can result in minute metal particles breaking off from the surfaces during jarring operations which can jam or damage the piston assembly and other moving parts.